1. Field of the Invention
The present invention relates to a receiving system of a data transfer, and more specifically to a receiving system for regenerating data included in a received signal using a parameter included in the received signal.
2. Description of the Related Art
Recently, in an equipment unit such as a television receiver (TV), a set top box (STB), a DVD player, etc., a high definition multimedia interface (HDMI) standard has become widespread. The HDMI standard adopts, in a physical layer, a digital visual interface (DVI) having a copy protection function of baseband digital contents outputted from the STB for receiving a digital broadcast, the DVD player, etc., and transmitting visuals and audio via a single cable. Especially, immediately before the entire conversion from an analog broadcast of a television broadcast to a digital broadcast, a data transmission in accordance with the HDMI standard (hereinafter referred to as an “HDMI transmission”) has become widespread mainly by the TV having a large screen flat panel display such as a liquid display, a plasma display panel (PDP), etc.
In the HDMI transmission, a clock signal for audio data is not directly transmitted from a transmission system to a receiving system, and a parameter used in generating a clock signal for audio data (hereinafter referred to as a “clock parameter”) is transmitted from the transmission system to the receiving system. The receiving system generates a clock signal for audio data using a clock parameter (refer to National Publication of International Patent Application No. 2005-514836 as an example). That is, the receiving system generates a clock signal having the same frequency as the clock signal for audio data used in the transmission system (hereinafter referred to as a “transmission end audio clock signal”) using a clock parameter, and regenerates audio data in synchronization with the generated clock signal. A clock parameter is included in an audio clock regeneration (ACR) packet transmitted at video blanking intervals. A “video blanking interval” is a period in which a signal containing no image data is transmitted. A clock signal for audio data generated by the receiving system using a clock parameter is hereinafter referred to as a “reception end audio clock signal”.
In the HDMI transmission, audio data is transmitted also in a packet at the video blanking intervals. The audio data transmitted to the receiving system is stored in the first-in first-out system memory (hereinafter referred to as “FIFO memory”) of a buffer and other units, and then the audio data is read from the FIFO memory in synchronization with the reception end audio clock signal. As a result, the audio data is regenerated as continuous audio.
If the amount of audio data stored in the FIFO memory in a predetermined time period matches the amount of audio data read from the FIFO memory, then the data storage rate of the FIFO memory is kept constant. The “data storage rate” refers to a ratio of the amount of data actually stored to a total amount of data that can be stored in the FIFO memory.
However, when the storage rate at which the audio data is stored in the FIFO memory does not match the read rate at which the audio data is read from the FIFO memory, the amount of audio data stored in the FIFO memory does not match the amount of audio data read from the FIFO memory. That is, when the amount of audio data stored in the FIFO memory is larger than the amount of audio data read from the FIFO memory, the audio data transmitted from the transmission system cannot be stored in the FIFO memory, and an overflow of the FIFO memory occurs. On the other hand, when the amount of audio data stored in the FIFO memory is smaller than the amount of audio data read from the FIFO memory, the amount of audio data stored in the FIFO memory gradually decreases, the audio data cannot be read from the FIFO memory, and an underflow of the FIFO memory occurs. That is, when the storage rate does not match the read rate, the data storage rate of the FIFO memory fluctuates.
In addition, there are the cases in which the transmission of audio data is temporarily stopped by a fault and other reasons of the transmission system, and audio data is dropped by a transmission error. In these cases, although the storage rate matches the read rate, the amount of audio data stored in the FIFO memory of the receiving system suddenly decreases, and the data storage rate of the FIFO memory drops. If the data storage rate drops, and the storage rate matches the read rate, then the data storage rate of the FIFO memory does not recover. When an overflow or an underflow occurs by an extreme decrease of the amount of audio data stored in the FIFO memory, the regenerated audio data becomes discontinuous, thereby degrading the quality of the audio.